Learn about your LTG - Fuel System
If the turbo is the LTG’s lungs, the fuel system is its heart — pumping precisely measured fuel into the combustion chamber at exactly the right time, under extreme pressure, thousands of times a minute. And unlike older systems, the LTG uses a fully electronic, returnless, on-demand fuel system that not only improves performance but also keeps emissions low.
By eliminating a return line from the engine to the tank, it avoids heating the fuel unnecessarily. Cooler fuel means reduced vapor generation inside the tank, which helps with both environmental compliance and fuel density (more oxygen-rich fuel under boost).
1. The Main Players in the LTG Fuel System
1. Fuel Pump
Inside the tank sits an electric, turbine-style low-pressure fuel pump. This pump’s job is simple — get fuel from the tank to the high-pressure pump up front. But unlike old-school pumps that run at one speed, this one is smart-controlled by the ECM via a Fuel Pump Flow Control Module (FPFCM).
Uses a PWM (Pulse Width Modulation) signal to precisely vary speed.
Runs only as hard as needed to maintain target pressure — saving energy and reducing heat in the tank.
2. High-Pressure Fuel Pump (HPFP)
Mounted on the engine and mechanically driven by the camshaft, the HPFP takes low-pressure fuel and cranks it up to over 2,000 psi (or more under high load) for direct injection.
Variable-pressure output, depending on load, boost, and tuning.
ECM controls injection timing and duration to the microsecond.
3. Fuel Injectors
These aren’t the pintle-style injectors of the 90s — they’re multi-hole, high-precision direct injectors that spray a fine mist directly into the combustion chamber.
Allows leaner mixtures under cruise and richer mixtures under boost without sacrificing driveability.
Critical for both performance and emissions control.
4. Fuel Tank
Located in the rear, the LTG’s tank is high-density polyethylene (HDPE) with a saddle design, allowing the driveshaft to pass through the center.
This shape requires careful fuel transfer between sides — handled internally by the module.
5. Fuel Pressure Sensor
Found on the feed line before the HPFP, this sensor gives the ECM constant pressure feedback for closed-loop control.
6. Fuel Level Sensor
A float arm and resistor setup that sends real-time fuel level data to the ECM, which relays it to your gauge.
7. Fuel Rail Assembly
Bolted directly to the cylinder head, it evenly distributes high-pressure fuel to all injectors and houses the fuel rail pressure sensor.
2. How It All Works Together
Here’s the flow:
Low-Pressure Side – The in-tank electric pump pushes fuel forward to the HPFP. Speed is controlled dynamically based on ECM commands through the FPFCM.
High-Pressure Side – The HPFP raises fuel pressure to extreme levels and feeds it into the fuel rail.
Injection – The ECM tells each injector exactly when and how long to open, based on boost, throttle, temperature, and sensor data.
Feedback Loop – The fuel pressure sensor constantly checks system pressure. If it drops or spikes, the ECM adjusts pump speed or injection timing instantly.
3. Fuel Metering Modes You Didn’t Know About
The LTG fuel system doesn’t just “on/off” the injectors. It changes strategy based on conditions:
Starting Mode – Adds extra fuel to fire up cold engines.
Clear Flood Mode – Cuts fuel during WOT cranking if the engine is flooded.
Run Mode – Maintains a stoichiometric mix for efficiency.
Acceleration Mode – Adds fuel for power and knock protection.
Deceleration Mode – Cuts fuel to save gas and reduce emissions.
Battery Voltage Correction Mode – Adjusts injector timing when electrical voltage fluctuates.
Fuel Cutoff Mode – Used in rev-limiter or overrun conditions.
On top of this, the ECM constantly watches short-term and long-term fuel trims using oxygen sensor feedback, adjusting in real time for altitude, ethanol content, or even small leaks.
4. Why This Matters for Modding & E85
If you’re running higher boost or switching to E85, the LTG’s direct injection system demands more from the HPFP and injectors. E85 requires about 30% more volume than gasoline, so fueling capacity becomes the limiting factor fast.
For mild E85 blends, the stock system can manage — but for full E85 and higher boost levels, you’ll want:
Larger injectors
Upgraded HPFP
Larger Fuel Lobe (Camshaft)
Possibly an auxiliary fuel system or port injection to prevent lean-out at high RPM/load.
5. DIY Maintenance Tips
Fuel filter: Even though GM says “lifetime,” replacing it at 60–80k miles keeps pressure stable.
Listen for pump noise: A whining in-tank pump is a warning sign — don’t ignore it.
Check fuel trims: A simple scan tool can reveal if your system is over- or under-fueling.
Use quality fuel: Poor-quality gasoline can clog injectors faster than you’d think.
Oil choice for E85/high boost: Use 0W-40 or 5W-50 to combat DI fuel dilution.
